Question: Solve for $x$ and $y$ using substitution. ${4x-y = -9}$ ${x = -y-11}$
Since $x$ has already been solved for, substitute $-y-11$ for $x$ in the first equation. ${4}{(-y-11)}{- y = -9}$ Simplify and solve for $y$ $-4y-44 - y = -9$ $-5y-44 = -9$ $-5y-44{+44} = -9{+44}$ $-5y = 35$ $\dfrac{-5y}{{-5}} = \dfrac{35}{{-5}}$ ${y = -7}$ Now that you know ${y = -7}$ , plug it back into $\thinspace {x = -y-11}\thinspace$ to find $x$ ${x = -}{(-7)}{ - 11}$ $x = 7 - 11$ ${x = -4}$ You can also plug ${y = -7}$ into $\thinspace {4x-y = -9}\thinspace$ and get the same answer for $x$ : ${4x - }{(-7)}{= -9}$ ${x = -4}$